When processing workpieces by means of an end effector on a manipulator, it is frequently required to continually move and thus position the operating point, which may also be referred to as the tool center point (TCP), of the manipulator during the machining process. In particular, if the manipulator is a multiaxis robot, the control of the manipulator is based on calculations performed in an NC controller, which include trajectory planning and interpolation, according to which the corresponding controls, for example, of the axes of the multiaxis robot, take place.
The calculations performed by the NC controller are based on various physical parameters of the manipulator, for example, lengths, weights, and other variables which are relevant to the calculations. However, in practice, these parameters are not ideally constant, but may change, for example, as a function of the instantane-ously prevailing temperature. If these changes are not taken into account when controlling the manipulator, a deviation results between the actual position of the operating point of the manipulator and the setpoint position of the operating point of the manipulator according to the calculation. Here and below, the term “NC controller” is to be understood in the broad sense, thus meaning a controller which comprises some or all functionalities of a PLC (programmable logic controller).
A method and a device for compensating for a temperature-dependent change in position on a machine tool is known from the related art and specifically from the published patent application DE 10 2010 003 303 A1. Here, an NC controller cal-culates setpoint values for various linear axes of the machine tool. These setpoint values take into account a temperature compensation which is based on instanta-neous temperature measurements and which ascertains a compensation value for the individual setpoint values of the respective linear axes and applies it to them. However, the compensation values are not only temperature-dependent; they also depend on the position of the linear axes. Thus, it is also taken into account that for precise temperature compensation, a position-dependent component must also be taken into account. To be able to perform the compensation in a timely manner specifically in the case of rapid changes in position, the compensation is determined via a system of fixed coefficients, which are applied to the measured temperatures and the axis positions, according to the determination via the NC controller.
However, the related art has the disadvantage that, despite the attempt to compensate by taking into account the temperature, whether as a function of position or independently of position, a deviation may result between the setpoint position and the actual position. This may be because the prevailing boundary conditions, for example, during an initial calibration carried out simultaneously in the laboratory for ascertaining the above coefficients, no longer exist. Thus, for instance, a specific temperature distribution may exist along a route of the manipulator, which cannot be sufficiently differentiated even by means of multiple distributed temperature sensors; or process forces acting on the manipulator may generate a significant influence on the position of the manipulator. Deviations which have their cause herein cannot be compensated for under the approach from the related art.